Altitude control system for automatic pilots



Sept. 11, 1951 P, TURNER ALTITUDE. CONTROL SYSTEM FOR AUTOMATIC PILOTSFiled April 50, 1947 E 0 W A mm m I. E H A fiwbsrhqw T 4 1 1 l 1 D1 \%.w1% w w N Q W A A Q. N 0 W E m Nu w E a W Q A NN Wm NNQ wmivw Nw\\ N TL rA mm E III |l WITNESJ Patented Sept. 11, 1951 2,561,8 1 ALTITUDE CONTROLSYSTEM FOR N91,"; eoiji'eretidrf'of New Jri epineeeeiei *aif craft aridjfer ehtibumg the rate at tvhih it is desired t'ieli r iipbr dive seiderererp.

In fiheibarbmetrie. dey1pes heretofore used fer this purposeQdifiieulties' have beii er'ieofinter'ed due to inher r' t instability, resultingin' hunting eein uene nd losfs'fdf'gbhtrdl'." It is et prima ygobjectefthis inve tion, therefpr e, to provide :ar'i mprevea flightlevel coh'trbl system which is 'sub's'tantilfly'fre fi'dm adverse h n fiQtv .4 Y. t. ether Object of this i ventien is to provigle a deviewhichmefy 'be used with an a'utdriiatit pilot t5 assist r te'niporliriljy 'rel'ievethe ,h'l'irria'ri Pilot iii iabhiiig'hfid/Bi r'rieihtia'ifh'g a die Ei l ud V. A further object gf this invention is to previde a device 'vvhi c h, in'YespOhse ff) perorn et ric pre's sure'changes, seiids memes 'e'f qperetihg'sigriiljs to the breeessilig jystemetain eatememegyjre- PHD-t A still furt er ob e t .Q thi i v i is t prbvide, ih' epnibifi'altieii, two 'eee'p'erative 'cq'nt1b1 units toobteinifi e'd eecuife'cy Withfiuts' c .rlfi of stability. M With thetbove and ether bjects in view, as will hereinafter epbear'fthirive'fltion' comprises the devices, ombinations 'and'arrangeni'ehts Qf.parts herinafterset f rth and illustrated in theacconipenyiiigschematic drawing of a preferred embodiment 'oftheinvehtion'ffrcim which the features thereof and the advantagesattaineii thereby will be readily understood py thesei iii g in the art.V .The aecompa nyi g drawing is a schematic wiring diagram of the systemembodying the invention.

In the single figure, the twp copperetiv e cpntrol devices' are" shown.A stabilizing unit 1 bm rise n ai cha be tamed by 'JQQ tainer 3,preferably of thermerinsulating h ete'ri'zil, and provided with'faflexible jmemhrgr e diaphragm 4, the piev ement ofwhich is' r- 1947,Serial No. 744,921 (01.14 .4)"

"I i iqeaimpeph re ik t u jh a va ve. 5 which spring-biased to an Oi'i'h'bositi'on "bufivihieij may 12? 9 9 29 9! PR WQQ 91 a il ui ,5 P ess e if sp ings I,

am mer e application, Serial No. 636,238, filed December 20, 1945, towhich reference may be had for a more complete explanation thereof. Itis sufficient here to note that the terminal 45 connects to the negativeor grounded side of the D.-C. supply, the terminal 48 connects to thepositive side ofthe Dg-C. supply and the terminals 46 and 41 are forconnection to proper processing coils 63 and 63 to give an up and a downsignal, respectively, to the aircraft elevator servo-motor. It isunderstood that the intensity of the signals is proportional to thestrength of the currents and resistors 49 and 50 employed to limit andadjust the precessing-coil currents by means of taps I, 5'2, 53 and 54thereon, as will presently be apparent.

Except for the specific electrical connections,

the above describes a schematic embodiment of a part of this inventionwhich will now be used for explaining the operation thereof, thenecessary electrical connections being pointed out as the explanationproceeds. Let us first consider the operation of the stabilizer unit Ias an assist pilot. In this case, when the human pilot Wishes tomaintain automaticallythe altitude at which he is flying, he turns ontheunit at that altitude. This is accomplished by applying positive andnegative battery voltage to the terminals 48 and 45 respectively. Thiscauses current to flow from the terminal 48 through a conductor 55 tothe contact 3I, thence through the bridge 33 to the contact 32, aconductor 56, and the coil 8 to ground, thus completing the circuit. Therelay 1 picks up and closes the valve 6. A second circuit is traced fromthe terminal 48 through a conductor 51 t0 the contact 31, thecontact 38,the conductor 58, the contact 43, the contact 44, a conductor 59.through the coil I2 to ground. Thus, the relay II also picks up andcloses the valve IIJ. With valves 6 and I0 closed, the chamber 2 iscompletely sealed from the atmosphere.

It will be observed that, at the time when the stabilizer unit I wasturned on, pressures equal to the atmospheric pressure at the altitudedesired existed on both sides of the diaphragm 4 and it was, therefore,balanced in its neutral position with the contact arm I1 midway betweenthe contacts 21 and 28. The aircraft continues in its original attitudewhich, let us assume, for example, is a dive, and the pressuredifferential on the diaphragm 4 causes the contact arm I1 to lower and,after sufficient altitude change, to make contact with the contact 28.When this occurs, a curren circuit is set up from the terminal 48through the conductor 51, a conductor BI], the contact arm I1, thecontact 28, the spring 22, and the tap 53', thence through a largeportion of the resistor 50 and conductors 6| and 62 to the terminal 46and through the precessing coil 63 (on the automatic pilot) to ground.This causes slow precession of the gyro unit, as explained in mycopending application referred to above, and the elevator controlsurface is operated so as to urge the craft into a climb. The craftthenbegins to level off but may still lose altitude causing furthertravel of the contact arm I1 until the contacts 29 and 30 close. lishedfrom the terminal 48 through the conductors 51 and 60, the contact armI1,'the contacts 28, 29 and 30, the spring contact 23, a conductor 64,and the coil 4llto ground. The relay 39 picks up and separates thecontacts 43 and 44, thereby interrupting the current to the coil Whenthis occurs, a circuit is estab- I 4 I2, and dropping out the relay II.This opens the valve I0, whereupon air begins to leak from theatmosphere into the chamber 2 past the restriction I4, thus tending toequalize the pressures acting on opposite sides of the diaphragm 4. Atthe same time, the relay contacts 4| and 42 are made and a circuit isestablished from the terminal 48, through the conductor 51, contacts 42and M, thence by way of a conductor to the tap 54 and through a smallportion of the resistor 50, through the conductors BI and 62 to theterminal 46, thence through the precessing coil 63 to ground. Thislatter circuit provides increased strength for the current to theprecessing coil and causes an increased precession rate withconsequently greater corrective movement of the aircraft elevator. Thiscondition of inceased current strength or fast climb signal can persistonly so long as the rate of change of atmospheric pressure is greaterthan a value determined by the air leak rate manually set by the knobI3. When the aircraft has reduced its dive rate to this predeterminedvalue, the pressures on diaphragm 4 are such that contacts 29 and 30just open. This again closes valve III, and the above-described processwill be repeated intermittently until the aircraft is in sufficientlylevel flight so that the pressure change is insufiicient to reclosecontacts 29 and 30 any more. The opening of the adjustable leakconstitutes a recalibration, of the stabilizer instrument in the sensethat a new reference altitude is continually being established while theleak is open, and the new reference altitude is always closer to theactual present altitude of the aircraft than was the original referencealtitude.

The aircraft normally should level off soon after the fast climb signalis sent to the pilot, and reverse movement of the diaphragm shouldbegin, thus turning off the air leak and resuming the slow precessionrate. However, in the event that the aircraft does not rapidly level offafter the fast climb signal is initiated, further decrease in altitudecauses sufficient movement of the contact arm I1 to break the contactbetween the contact 32 and the bridge element 33, whereby current to therelay coil 8 is interrupted. The relay 1 drops out and opens the valve 6connecting the chamber 2 directly with the atmosphere. This tends toequalize the diaphragm pressures very rapidly and establishes a newreference altitude at the existing value, and thus relieves the craft ofthe necessity of climbing appreciably before coming to level flight. I

With the above arrangement, a small signal produces a low rate ofprecession and is accompanied by low hunting. Valve II] remains closedand there is minimum drift from the reference altitude. A large signalproduces a high rate of precession but, with the air bleed through valveI0, is accompanied by desirably low hunting.

It is to be noted that the provision for bleeding air to or from the airchamber and for directly venting said chamber decreases the accuracy ofresponse of this system but, at the same time, improves the stabilitythereof because it provides an anticipatory action which preventsover-response of the system and results in reduced hunting.

It is clear that the knob I3 may be adjusted to establish an optimumvalue of bleeding rate for given conditions and minimum hunting.

Obviously, the above described instrument may be made operative orinoperative from "a 5 :bya'adiantenergy icontrol when to desired:throughmontrol of .the power supply thereto; The stabilizing unit I,described .aboue, my be operated :as a single instrument in com notionwith an automatic .pilot to effect auto: matic altitude control {oraircraft.

A second control ,device .65, called .a sensing may :be :usedincooperation with the .stabilizing unit l rset .forth above and, incombinar tion therewith, provides a more positive sense reference andenables .anyaltitudefiand a maximum rate of climb tobe preset in'thesystem. The sensing .device (comprises a closed isylphon e'bOHOWS lil,evacuated andspring loaded so that increased altitude causes veimansionthereof. 'sylphon bellows El-is anchored :at one iengi to a supporting.frame 68 and carries .at the endthereof .a ram 69. The stationary;frame 8 is iormed with .a boss SLO which provides .a

bearing for a lead screw :ll, cperatedsby turnin aknob 12. Atravelingnut '13,.threaded onto lead screw H,: may,pbe,positioned at anypoint :along the support 58 by manipulation of the knob 12.

Located .onan axis .H, fixed with respect to l the irame 68, is..amagnetic plate :15, f ree1nor.- molly to :turnabout said axis butwhich'maybe looked in any angular position by exciting an attractingsolenoid, indicated schematically :as '36. V -secured to, but insulated:f-rom, the :plate arespaced contacts 11 and 1.8. on axis .14 is a.spring contact L9, :nosltionfil ii'ntermediate saidspaced contactsll and1.8, and *biased in position, as shown ;by atension spring J0.

-Anrarm 8|, secured to the .plate 15, is extended tocontact the.traveling'nut l;3:against which it :urged due to the bias force of thespring lO, acting .through .the. contact 19 and the plate 115. .Thespring :contactflS :andgone endgof the solenoid 16 areconnected byavcondll m 821m in :terminal .83 ,to which the positive battery -voltageisappliedwhendtis desired ;to cut in :the sensing unit.

The contact 11 is rconnectedby a conducto dtto arheostat :85 and theme,.by a conductor 206, ate the terminal 114:6. Simi,1ar1,y,zthecontact-l.8:-is co nnected by ,a conductorjfl to a rheostat 88 and thence, by aconductor 8.9;to1thetermi- :It will be seen that 1 longitudinal movementof ram 189 in l-response t0 'pressurechange, due to increasingialtitllde ,for example, ultimately causes-movement ofthe spring contact9 land, lifnthemlate 15=and thecontacts Hand 18 are held stationaryby-thesolenoid 76, the contact .10 will: move outof contact with thecontact H ;and into-contact with the contact 18.

,It-is clear that, since motion of therami-GQ .dependent uponaltitudechange, an altitude isoale 68' may be marked out along the support-ll,.-as shown, so that the plate '15 with the con- .tacts'" and 18 maybe preset, by manipulation of (the knob '12, to cause switching atapredetermined altitude.

.=The,. rheostats .85 and Y88 are used for control-" .lingtthemagnitudes of thercurrentsupplied to theprecessingcoils by the sensingunit '66, .as

.be explainedpresently.

Let us assume that the humanpilot desires to have the aircraftclimbautomatically to a preedeterminedaltitude.andilevel off there. To dothis, hewill turn .on both stabilizing and sens- .inginstruments withthe, latter preset for the .fleslredaltitude as provided. Since thecontacts 11 and 19 are closed, current will traverse the ,Also pivotedwith the contact :21.

aircraft wou d ,lo p r r ically o so int a stall,

neither of which is desirable.

-,To prevent this, the stabiliding unit prQvides a counter precession tobalance th t c eated @by the sensin unit. For example, as the amoral-iclimbs, :responsively to -.the si nal from thesensting :unit, -.thediaphragm 4 .Qf :the stabilizer unit moves outwardly responsiveeto.ldeqreasing pres.- sure and the contact larrn 1L1 makes contact Th sestabl shes a current feed of small magnitude throu h itheprcc s gn coil'63. 'While this counter precession as at :normally great enough :tovovercome -;-that produced .by the .coil :53, it does immediatelydecrease the net precession causing climb.

'ther increase in altitudeflcauses further move.- ment .of the diaphragm.-.,4 and the contact arm I! until the contact 26 closes .withthe:oritaq -.2 5. This establishes iaecircuit :from the 1 terminal '48,through the .-conductorsa5:'l rand :60,- -the$ 71? I l, the contacts:2.=1,:246aa nd 25,:the contact-spring -20, thenceibya conductor 19.0through the coil to ground. The relays picks up andseparates thecontacts 7 3 I .and 138 which, as explained hereinbefore, opens thebleed-yalve J0 tostart pressure equalization onl-opposite-sidcsmf the.dlaphragm 4. At the same time, the-Contacts 36 and 31 close toestablish .a circuit-fromrthe'ter- :minal 48, :through the conductor"51. the con- ;tact arm v3'1, the contact 35 and .a conductor 9i tothertap 5|, thence'through a small portion of the resistor 49 and ,aconductor 92 to the terminal and through theprecession coil 6:3 toground. Thetap-5l is normally .so adjusted that the current to thecoil\63 is greater: than thatto the coil- 63 from the asensingunitesignal.

That is -to say, the counter precessionzis;-now

sufiicient to overpower the eprecession .lc'ausing climbresul'ting in alesser rateof clim-bof the aircraft. This will persist until thepressure. dif- "ference on opposite sides of the diaphragm Avis lowereddueto the air bleed to causel thecontact arm I! toopenthe contacts :25and 1:26, whereupon the climb signal from the sensing unit will againpredominateand the rate ofrclimb again "increases, and theforegoingsequence .of

events Will-repeat itself. This automatic intermittent operationcontinues until the preset alti -tude is reached, whereuponthe ram 69contacts the arm 19 and breaks contact-with the contact '11, ---thusdestroying 'theconstant climbs-signal from-thesensing unit. Itwill beobserved from the above description that the --combination,=.of-the-constantsignal -"from the sensing. unit with the periodic countersignal from t the stabilizing unit, 'applied as-a function of the air.bleedrate,

"limits and controls the rate of climb or dive -and, by properadjustments. of bleed rate why 70,

manipulation of knob 13 and of i the precession coil current values bytaps 5 I, 552, r 53 .-and :54, and rheostats-85 and 88,'thesemaximums-rates invention, actually -per1orms a double function,

When the stabilizing unit is used alone, the bleed rate providesanticipatoryaction and prevents overtravel and reduceshunting. When thesensing unit is addedto the system, the bleed rate also functions tolimit'the maximum rate of climb or dive to prevent stall and loss ofcontrol. As explained above, the stabilizing unit may automaticallyrecalibrate itself to an altitude different from that desired; and thisis done to prevent hunting, but, at the same time, decreases theaccuracy of response. The sensing unit helps to regain this accuracy byacting as an altitude monitor. If, due to excessive operation of thebleed valve, the stabilizing unit urges levelling off at an altitudesufiiciently different from that desired, the sensing unitwill not besatisfied but will continue to signal the automatic pilot for a climbora dive untilthe desired altitude-is attained.

In cases of remote control, where the preset feature is not desired, thepilot may turn. on the sensing unit by radio means at any altitude it isrequired to maintain. This act of turning on the unit causes thesolenoid 16 to lock the'plate l in position to monitor the altitude ofthe aircraft to the value existing at that time. Further, thetraveling'nut 13 may be set to some minimum altitude value, as desired,under certain circumstances.

It is desirable that the manual control of the auto-pilot by means-ofthe regular controlstick, ."as described in my copending applicationreferred to above, shall. have priority over the control by the presentstabilizing and sensing units and this may be readily provided byproperly adjusting the relative strengths of the currents to theprecessing coils.

Having thus set forth the nature of the invention, what I claim hereinis:

1. In an altitude control system for aircraft having a .gyroscope andgyroscope-precessing means for maneuvering said gyroscope, means aresponsive to the atmospheric pressure for urging continuous actuationof said precessing means until a predetermined altitude is reached, andmeans for intermittently modifying the actuation provided by said firstmeans in response to the rate of change of said atmospheric pressure.

2. In a flight level control system for aircraft having a gyroscopecontroller and means for precessing said gyroscope controllerformaneuvering said aircraft, a first means rendered effective upon achange of atmospheric; pressure for continuously actuating saidprecessing means and .second means rendered effective at intervals and-for a length of time in each interval dependent on the rate of changeof atmosphericpressure for modifyin the actuation of said precessingmeans by said first means. 1 ,3. In a control system for aircraft havinga gyroscope and separate means responsive to electric current forcausing opposite precession of said gyroscope forqmaneuvering saidaircraft, first means responsive to the departure of the atmosphericpressure from a predetermined value for initiating a first current inone of said precession-causin means, second means responsive to theresulting corrective change of atmospheric pressure for intermittentlyinitiating a second current in the other of said precessioncausingmeans, and third means for causing said second current to persist eachtime it is initiated only so long as the rate of change-of saidatmospheric pressure exceeds a predetermined value.

.4. In a control system for aircraft having a .control gyroscope andmeans for precessing said gyroscope for maneuvering said aircraft,imeansrendered effective upon small changesin atmospheric pressure foractuating said precessing means at a low rate, means responsive tolarger changes in atmospheric pressure for intermittenly actuating saidprecessing means at a higher rate and means for maintaining said highrate at each actuation responsively to the rate ,of change of saidatmosphericv pressure.

' 5. In a control system for aircraft having gyroscope-precessing means,means renderd effective upon small changes in atmospheric pressure foractuating said precessing means at a low rate, means responsive tolarger changes in atmospheric pressure for actuating said precessingmeans at a higher rate and means for maintaining said higher rate ateach actuation as long as the rate of change of atmospheric pressureexceeds a predetermined amount.

6. In a, control system for aircraft, and air chamber, a movablediaphragm separating the interior of said chamber from the atmosphere, afirst, normally-open duct connecting said chamber with said atmosphere,a second, normallyopen duct connecting said chamber with saidatmosphere, means for closing said ducts, means responsive to smallmovements of said diaphragm for opening said first duct, meansresponsive to larger movements of said diaphragm for opening said secondduct, and means for adjusting the rate of air leak through said firstduct.

7. In an automatic control system for aircraft havinggyroscope-precessing means for maneuvering said gyroscope to controlsaid aircraft, sensing means effective, responsive to a departure of theatmospheric ressure from a predetermined value, to actuate saidprecessing means, stabilizing means, including first means effective,responsive to a change in atmospheric pressure of a predetermined smallamount, to modify said actuation of the precessing means, and secondmeans effective, responsive to a change in atmospheric pressure of apredetermined larger amount, to further modify said actuation of theprecessing means, said second means being intermittently effective tolimit the time rate of change of altitude of the aircraft to apredetermined amount.

8. In an automatic control system for aircraft having first and secondcurrent-responsive gyroscope-precessing means for controlling saidaircraft, sensing means rendered effective, responsively to a departureof the atmospheric pressure from a predetermined value for establishinga corrective electric current in said firstgyroscope-precessing means,stabilizing means, including first means effective, responsively to achange in atmospheric pressure of a predetermined small amount, toestablish in said second gyroscope-precessing means an electric currentsmaller than that established in said first gyroscope-precessing means,and second means effective, responsively to a change in the atmosphericpressure of a predetermined larger amount, to establish in said secondgyroscope-precessing means an electric current larger than thatestablished in said first gyroscope-precessing means, said second meansbeing intermittently effective to limit the rate of change of altitudeof the aircraft to a predetermined value.

9. In an automatic control system for aircraft having agyroscope-precessing means for maneuvering said aircraft, sensing meanseffective,

iresponsively to a departure of the'atmospherlc pressure from apredetermined value, to send a. first signal to said precessing means, astabilizing means effective, responsively to a change of the atmosphericpressure, to send a second signal to said precessing means having aneffect on the precession opposite to that of said first signal, meansfor increasing the strength of said second signal responsively to apredetermined change of the atmospheric pressure and means responsive tothe time rate of change of said atmospheric pressure for intermittentlyre-establishing said signal of increased strength.

10. In an automatic control system for aircraft havinggyroscope-precessing coils for controlling said aircraft responsively toelectrical currents in said coils, means responsive to changes inatmospheric pressure for applying current to a selected one of saidprecessing coils, means responsive to the direction of said changes inatmospheric pressure for selecting the proper coil for the currentapplication, means responsive to larger changes in atmospheric pressurefor producing increased currents in said gyroscope-precessing coils,means for intermittently maintaining said increased currents to limitthe rate 01' change of altitude of the aircraft to a predetermined valueand manual means for setting said predetermined value. a

11. In an automatic altitude control system for aircraft having acontrol gyroscope and means for precessing said gyroscope,pressure-responsive means for causing said precessing means to urgecontinuous precession of said gyroscope until a predetermined altitudeis reached, means responsive to a change of pressure to urge a decreaseof the rate of said precession, and means, responsive to a larger changeof pressure, for intermittently urging a reversal of said precession,said last urging means serving to limit the time rate of change ofaltitude of the aircraft to a predetermined maximum value.

EDGAR P. TURNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,152,144 Minelli Mar. 28, 19392,167,077 Koster July 25, 1939 2,191,250 Fischel Feb. 20, 1940 2,315,501Crane et a1 Apr. 6, 1943 2,443,748 Sanders, Jr., et a1. June 22, 19482,459,495 Brown Jan. 18, 1949

